zFTPServer is a powerful yet generally easy-to-use FTP server.
The program supports regular FTP and both host and IP-based passive mode. It runs as a system service for improved reliability, and includes plenty of useful security features.
So, for instance, enabling "Anti-Hammering" allows you to ban particular IP addresses if they make more than a set number of connections within a short period of time. Or, if you want to keep the server private, then you can choose to allow only connections from the IP addresses that you define.
Other interesting options include the ability to schedule global speed limitations, so you might limit upload speeds, download speeds or both during the daytime, to avoid the server hogging all your bandwidth, then remove the restrictions at night (or any other time when you're not around).
Please note, this free version of zFTPServer is only one of those made available by the authors.
The next version up, Personal, adds encrypted remote administration, automatic updates, scripting and FTPS support. The Professional version includes upload balancing and FXP support for site-to-site transfers. The Corporate version adds Active Directory integration, while zFTPServer Enterprise supports TFTP and SFTP with public/ private key integration. Prices range from 9.99 to 499 Euros, and you can find out more on the product site.